Optical pickup device and optical disk apparatus

ABSTRACT

A half-wave plate is attached to a lens holder to integrally drive a collimator lens and the half-wave plate. When the lens holder is moved to a servo position, the half-wave plate is inserted in and retracted from an optical path of a laser beam. Therefore, the laser beam is formed in S-polarized light or P-polarized light with respect to a polarization beam splitter, and the laser beam is guided to a first objective lens or a second objective lens.

This application claims priority under 35 U.S.C. Section 119 of JapanesePatent Application No. 2007-022867 filed Feb. 1, 2007, entitled “OPTICALPICKUP DEVICE AND OPTICAL DISK APPARATUS”.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical pickup device and an opticaldisk apparatus into which the optical pickup device is incorporated,particularly to a compatible type optical pickup device sorting a laserbeam emitted from a common light source into two objective lenses and anoptical disk apparatus into which the optical pickup device isincorporated.

2. Description of the Related Art

Currently, there are two optical disks, i.e., BD (Blu-ray Disc) andHDDVD (High-Definition Digital Versatile Disc), in which a laser beamhaving a blue wavelength is used. Because BD and HDDVD differ from eachother in a thickness of a cover layer, two objective lenses compatiblewith BD and HDDVD are provided in the optical pickup device compatiblewith both BD and HDDVD, and the laser beam having the blue wavelengthemitted from one semiconductor laser is sorted into the objective lensesby an optical system respectively.

A liquid crystal cell and a polarization beam splitter can be used as aconfiguration in which the laser beam is sorted into the two objectivelenses. In the configuration, a polarization direction of the laser beamis changed into one of P-polarized light and S-polarized light withrespect to the polarization beam splitter by the liquid crystal cell. Inthe case of P-polarized light, the laser beam is transmitted through thepolarization beam splitter and guided to a first objective lens. In thecase of the S-polarized light, the laser beam is reflected by thepolarization beam splitter and guided to the first objective lens.

However, in the configuration, cost of the optical pickup device isincreased because the liquid crystal cell is used as a function forsorting the laser beam into the two objective lenses. Unfortunately, aproblem arises that the laser beam strength is attenuated when the laserbeam passes through the liquid crystal cell. Additionally, it isnecessary that circuits and configurations for controlling drive of theliquid crystal cell be separately provided to guide the laser beam towhich objective lens.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, an optical pickupdevice includes a laser source which emits a laser beam having apredetermined wavelength; first and second objective lenses which causethe laser beam to converge onto a recording medium; a polarization beamsplitter which is disposed between the laser source and the first andsecond objective lenses; first and second optical systems which guidethe two laser beams split by the polarization beam splitter to the firstand second objective lenses respectively; first and second opticalelements which are disposed in the first and second optical systemsrespectively, the first and second optical elements being moved inoptical axis directions of the laser beams to adjust opticalcharacteristics of the laser beams respectively; a first actuator whichsupports a first holder holding the first optical element while thefirst holder can be displaced in the optical axis direction of the laserbeam; a second actuator which supports a second holder holding thesecond optical element while the second holder can be displaced in theoptical axis direction of the laser beam; a driving portion whichimparts a driving force to the first actuator; a transfer mechanismwhich transfers the driving force to the second actuator such that adrive stroke is smaller than that of the first actuator; and a waveplate which is inserted in and retracted from an optical path betweenthe laser source and the polarization beam splitter to change thepolarization direction of the laser beam when the laser beam is incidentto the polarization beam splitter.

The first and second optical elements are moved in a direction in whichthe wave plate is inserted and retracted, the wave plate is disposed ina support portion integral with the first holder, the first actuatormoves the first holder in both a first stroke for optical characteristicadjustment with the first optical element and a second stroke exceedingthe first stroke.

The first holder is moved between the stroke for optical characteristicadjustment and the additional stroke to insert and retract the waveplate in and from the optical path. The polarization direction of thelaser beam incident to the polarization beam splitter is adjusted suchthat the laser beam is guided to the first optical system, when thefirst holder is located in the first stroke, and the second holder islocated in the stroke for optical characteristic adjustment with thesecond optical element while the polarization direction of the laserbeam incident to the polarization beam splitter is adjusted such thatthe laser beam is guided to the second optical system, when the firstholder is located in the second stroke.

In the optical pickup device according to the first aspect of thepresent invention, the wave plate is inserted in and retracted from theoptical path using the first actuator driving the first optical element,and the target to which the laser beam is incident is switched betweenthe first and second objective lenses. Therefore, the need for theadditional configuration for driving the wave plate is eliminated toachieve the simple configuration of the optical pickup device. Becausethe inexpensive wave plate is used as the optical path switching part,the cost increase can be suppressed in the optical pickup device.

Additionally, the optical path of the second optical system can beshortened because the drive stroke of the second actuator is suppressedby stroke buffering action in the transmission mechanism. Therefore,even if the large optical path of the second optical system is notensured due to layout of the optical components, the second opticalelement can smoothly be driven by the common driving portion.

According to a second aspect of the present invention, the optical diskapparatus includes the optical pickup device according to the firstaspect of the present invention; and a servo circuit which controls thedriving portion to adjust the optical characteristics of the laser beamsincident to the first and second objective lenses, the servo circuitcontrolling whether the laser beam is guided to the first or secondoptical system.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further objects and novel features of the presentinvention will more fully appear from the following description ofembodiments with reference to the accompanying drawings, in which:

FIGS. 1A and 1B show a configuration of an optical pickup deviceaccording to an embodiment of the present invention; and FIG. 1C shows apolarization direction of a laser beam;

FIGS. 2A and 2B are views explaining a drive stroke of a lens holder ofthe embodiment;

FIG. 3 shows a circuit configuration of an optical disk apparatusaccording to an embodiment of the present invention;

FIG. 4 shows a configuration of a signal amplifying circuit of theembodiment;

FIGS. 5A and 5B are views explaining an operation of the optical pickupdevice of the embodiment;

FIG. 6 is a flowchart showing a reproduction operation of the opticaldisk apparatus of the embodiment;

FIGS. 7A and 7B show a modification of the optical pickup device of theembodiment;

FIGS. 8A and 8B show a modification of the optical pickup device of theembodiment;

FIG. 9 shows a modification of the optical pickup device of theembodiment;

FIG. 10 shows a modification of the signal amplifying circuit of theembodiment; and

FIG. 11 shows a modification of the optical pickup device of theembodiment.

However, the drawings are illustrated only by way of example withoutlimiting the scope of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described belowwith reference to the drawings. In the following embodiments, thepresent invention is applied to an optical pickup device and an opticaldisk apparatus compatible with Blu-ray Disc (hereinafter referred to as“BD”) and HDDVD (hereinafter referred to as “HD”).

An optical pickup device according to an embodiment of the presentinvention will be described with reference to FIGS. 1A to 1C. FIG. 1A isa plan view showing an optical system of the optical pickup device, andFIG. 1B is a side view showing a portion subsequent to upwardlyreflecting mirrors 19 and 24 of FIG. 1A when viewed from an X-axisdirection. In FIG. 1B, an objective lens holder 31 is shown by asectional view such that an internal structure of the objective lensholder 31 can easily be seen.

With reference to FIGS. 1A and 1B, a semiconductor laser 11 emits alaser beam having a wavelength of about 400 nm. A half-wave plate 12 isprovided to adjust a polarization direction of the laser beam withrespect to a polarization beam splitter 15. For example, the half-waveplate 12 is provided such that the polarization direction of the laserbeam becomes the direction of 45′ (arrow direction of FIG. 1C) withrespect to the polarization beam splitter 15 for the P-polarized lightand S-polarized light.

A half-wave plate 13 converts the polarization direction of the laserbeam into the S-polarized light with respect to the polarization beamsplitter 15 after the laser beam passes through the half-wave plate 12.A half-wave plate 14 converts the polarization direction of the laserbeam into the P-polarized light with respect to the polarization beamsplitter 15 after the laser beam passes through the half-wave plate 12.The half-wave plates 13 and 14 are disposed in a tongue piece 41 a of alens holder 41 holding a collimator lens 22. In the tongue piece 41 a,openings or notches are formed in positions where the half-wave plates13 and 14 are disposed such that the laser beam passing through thehalf-wave plate 12 is guided toward the direction of the polarizationbeam splitter 15.

The polarization beam splitter 15 transmits or reflects the laser beamincident from the side of the semiconductor laser 11 according to thepolarization direction of the laser beam. As shown in FIG. 1A, in thecase where the laser beam is transmitted through the half-wave plate 13,the laser beam becomes the S-polarized light and is reflected by thepolarization beam splitter 15. On the other hand, when the lens holder41 is displaced from the state shown in FIG. 1A toward a Y-axisdirection to cause the half-wave plate 14 to transmit the laser beam,the laser beam becomes the P-polarized light and the laser beam istransmitted through the polarization beam splitter 15.

After the laser beam (P-polarized light) transmitted through thehalf-wave plate 14 is transmitted through the polarization beam splitter15, the laser beam is reflected by a mirror 16, and the laser beam isconverted into parallel light by a collimator lens 17. Then, the laserbeam is reflected by a mirror 18 and the laser beam is reflected towarda direction of an HD objective lens 21 by the upwardly reflecting mirror19.

A quarter-wave plate 20 converts the light reflected from the opticaldisk into linearly-polarized light (S-polarized light) while convertingthe laser beam reflected by the upwardly reflecting mirror 19 intocircularly-polarized light. The linearly polarized light is orthogonalto polarization direction in which the laser beam is incident to theoptical disk. Therefore, the laser beam reflected from the optical diskis reflected by the polarization beam splitter 15 and introduced to aphotodetector 28. The HD objective lens 21 causes the laser beamincident from the side of the quarter-wave plate 20 to converge onto HD.

The laser beam (S-polarized light) transmitted through the half-waveplate 13 is reflected by the polarization beam splitter 15, and thelaser beam is converted into the parallel light by the collimator lens22. Then, the laser beam is reflected by a mirror 23, and the laser beamis further reflected toward a direction of a BD objective lens 26 by theupwardly reflecting mirror 24.

A quarter-wave plate 25 converts the light reflected from the opticaldisk into the linearly-polarized light (S-polarized light) whileconverting the laser beam reflected by the upwardly reflecting mirror 24into the circularly-polarized light. The linearly polarized light isorthogonal to polarization direction in which the laser beam is incidentto the optical disk. Therefore, the laser beam reflected from theoptical disk is transmitted through the polarization beam splitter 15and introduced to the photodetector 28. The BD objective lens 26 causesthe laser beam incident from the side of the quarter-wave plate 25 toconverge onto BD.

An anamorphic lens 27 induces astigmatism into the laser beam reflectedfrom the optical disk. The photodetector 28 includes a quadratic sensorin a light acceptance surface thereof, and the photodetector 28 isdisposed such that an optical axis of the laser beam reflected from theoptical disk pierces through an intersection point of two parting linesof the quadratic sensor. A focus error signal, a tracking error signal,and a reproduction signal are generated based on signals from thequadratic sensor.

As shown in FIG. 1B, the quarter-wave plates 20 and 25, the HD objectivelens 21, and the BD objective lens 26 are attached to the commonobjective lens holder 31. The objective lens holder 31 is driven in afocus direction and in a tracking direction by a well-known objectivelens actuator including a magnetic circuit and a coil. Usually the coilis disposed in the objective lens holder 31. In the objective lensactuator of FIG. 1B, only the coil 31 is shown and the magnetic circuitis not shown.

In the two collimator lenses, the BD collimator lens 22 is attached to alens holder 41. The lens holder 41 is supported by guide shafts 42 a and42 b provided in parallel on the support base, and the lens holder 41can be moved in an optical axis direction of the collimator lens 22. Theplate-shape tongue piece 41 a having a predetermined width in a Z-axisdirection of FIG. 1A is formed in the lens holder 41, and the half-waveplates 13 and 14 are attached onto one of the surfaces of the tonguepiece 41 a as described above.

A plate-shape portion 41 b which is elastically bent in the Z-axisdirection of FIG. 1A is formed in the lens holder 41, and a rack gear 44is provided in a lower surface of the plate-shape portion 41 b. On theother hand, a motor 45 is placed on the support base, and a worm gear 45a is formed in a rotary shaft of the motor 45. The motor 45 is formed bya stepping motor. The rack gear 44 provided in the lower surface of theplate-shape portion 41 b of the lens holder 41 is brought intopress-contact with the rotary shaft of the motor 45 so as to engage theworm gear 45 a. Therefore, when the motor 45 is driven, a driving forceof the motor 45 is transmitted to the lens holder 41 through the wormgear 45 a and rack gear 44. This enables the lens holder 41 to be movedin the optical axis direction of the collimator lens 22.

A guide shaft 42 a is inserted into a spring 43, and the lens holder 41is biased toward the direction of the motor 45 by the spring 43. Thebiasing force eliminates mechanical play of the motor shaft in alongitudinal direction.

The HD collimator lens 17 is attached to a lens holder 46. The lensholder 46 is supported by guide shafts 42 b and 42 c provided inparallel on the support base, and the lens holder 46 can be moved in theoptical axis direction of the collimator lens 17. Accordingly, the guideshaft 42 b supports both the lens holder 41 and the lens holder 46. Twosupported portions (hereinafter referred to as “second supported portion46 a and 46 b”) on the side of the lens holder 46 are provided so as tosandwich a supported portion (hereinafter referred to as “firstsupported portion 41 c”) on the side of the lens holder 41 in the Y-axisdirection of FIG. 1A. Predetermined gaps exist between the firstsupported portion 41 c and the second supported portions 46 a and 46 b.

A guide shaft 42 b is inserted into a spring 47, and the biasing forceof the spring 47 brings the lens holder 46 into press-contact with astopper 48 on the support.

FIGS. 2A and 2B are views explaining drive strokes of the lens holders41 and 46.

With reference to FIG. 2A, the lens holder 41 is driven in a range of astroke Sa during an aberration correction operation when BD is loaded inthe optical disk apparatus. In this case, the first supported portion 41c does not abut on the second supported portions 46 a and 46 b, but thefirst supported portion 41 c is moved between the second supportedportions 46 a and 46 b. In addition to the stroke Sa, a stroke Sbremains between the first supported portion 41 c and the secondsupported portions 46 a and 46 b.

When HD is loaded, the lens holder 41 is moved from the state shown inFIG. 2A across the stroke Sb to the lower portion of FIG. 2A. At thispoint, the first supported portion 41 c abuts on the second supportedportion 46 b in the middle of the movement, and the lens holder 41 isfurther moved to the lower portion of FIG. 2A, whereby the lens holder46 is moved to the position shown in FIG. 2B against the biasing forceof the spring 47. Therefore, the lens holder 46 is located at a positionwhere aberration correction is performed by the collimator lens 17. Thelens holder 46 is displaced in a range of a stroke Sc during theaberration correction operation.

FIG. 3 shows a circuit configuration of an optical disk apparatusaccording to an embodiment of the present invention, into which theoptical pickup device is incorporated. FIG. 3 shows only portionsconcerning the optical pickup device in the circuit configuration of theoptical disk apparatus.

A signal amplifying circuit 51 generates a focus error signal (FE), atracking error signal (TE), and a reproduction signal (RF) based on thesignal inputted from the photodetector 28. FIG. 4 shows a configurationof the signal amplifying circuit 51. As show in FIG. 4, the signalamplifying circuit 51 includes five adding circuits 101 to 104 and 107and two subtracting circuits 105 and 106. As described above, thequadratic sensor is disposed in the photodetector 28, Assuming that A toD are signals from the sensors A to D shown in FIG. 4, the focus errorsignal (FE), the tracking error signal (TE), and the reproduction signal(RF) are generated by computations of FE=(A+C)−(B+D), TE=(A+B)−(C+D) andRF=A+B+C+D respectively.

With reference again to FIG. 3, a reproduction circuit 52 reproducesdata by processing the reproduction signal (RF) inputted from the signalamplifying circuit 51.

A servo circuit 53 generates a focus servo signal and a tracking servosignal based on the focus error signal (FE) and tracking error signal(TE) inputted from the signal amplifying circuit 51, and the servocircuit 53 supplies the focus error signal (FE) and the tracking errorsignal (TE) to the coil 32 (objective lens actuator) in the opticalpickup device. In reproducing BD and HD, the servo circuit 53 monitorsthe reproduction signal (RF) inputted from the signal amplifying circuit51, the servo circuit 53 generates a servo signal (aberration servosignal) to drive and control the collimator lenses 22 and 17 such thatthe reproduction signal (RF) becomes the best, and the servo circuit 53supplies the servo signal to the motor 45 in the optical pickup device.

The servo circuit 53 supplies a signal to the motor 45 to locate thelens holder 41 at one of a first position and a second positionaccording to a control signal inputted from a microcomputer 55. At thefirst position, the half-wave plate 13 is inserted in an optical pathbetween the half-wave plate 12 and the polarization beam splitter 15. Atthe second position, the half-wave plate 14 is inserted in the opticalpath between the half-wave plate 12 and the polarization beam splitter15. Additionally, the servo circuit 53 supplies a signal for focuspull-in to the coil 32 (objective lens actuator) in the optical pickupdevice.

A laser driving circuit 54 drives the semiconductor laser 11 in theoptical pickup device according to the control signal inputted from themicrocomputer 55. The microcomputer 55 controls each portion accordingto a program stored in a built-in memory.

An operation of the optical pickup device will be described withreference to FIGS. 5A and 5B.

With reference to FIG. 5A, when BD is loaded in the optical diskapparatus, the lens holder 41 is located at the first position, and thehalf-wave plate 13 is inserted in the optical path between the half-waveplate 12 and the polarization beam splitter 15. At this point, thecollimator lens 22 is located at an initial position (predeterminedposition for forming the laser beam in the parallel light) in the strokeSa of FIG. 2A. When the half-wave plate 13 is inserted in the opticalpath, the laser beam is transmitted through the half-wave plate 13 tobecome the S-polarized light with respect to the polarization beamsplitter 15. Therefore, the laser beam substantially totally reflectedby the polarization beam splitter 15.

After the laser beam reflected by the polarization beam splitter 15 isformed in the parallel light by the collimator lens 22, the laser beamis reflected by the mirror 23, and the laser beam is further reflectedtoward the BD objective lens 26 by the upwardly reflecting mirror 26.Then, the laser beam is converted into the circularly-polarized light bythe quarter-wave plate 25, and the laser beam is caused to converge ontoBD by the objective lens 26.

The laser beam reflected from BD is transmitted through the quarter-waveplate 25 again, thereby converting the laser beam into thelinearly-polarized light orthogonal to the polarization direction inwhich the laser beam is incident to the optical disk. Then, the laserbeam reversely travels the optical path, and is incident to thepolarization beam splitter 15. At this point, the laser beam issubstantially totally transmitted through the polarization beam splitter15 because the polarization direction of the laser beam becomes theP-polarized light with respect to the polarization beam splitter 15.Then, the anamorphic lens 27 induces the astigmatism into the laserbeam, and the laser beam converges onto the light acceptance surface(quadratic sensor) of the photodetector 28.

In performing the reproduction operation to BD, the aberration servosignal is supplied to the motor 45, the collimator lens 22 is finelymoved in the optical axis direction in the aberration correction strokerange (stroke Sa of FIG. 2A) range, which suppresses the aberrationgenerated in the laser beam on BD.

With reference to FIG. 5B, when HD is loaded in the optical diskapparatus, the lens holder 41 is located at the second position, and thehalf-wave plate 14 is inserted in the optical path between the half-waveplate 12 and the polarization beam splitter 15. At this point, thecollimator lens 17 is located at an initial position (predeterminedposition for forming the laser beam in the parallel light) in the strokeSc of FIG. 2B. Therefore, the laser beam becomes the P-polarized lightwith respect to the polarization beam splitter 15, and the laser beamsubstantially totally transmitted through the polarization beam splitter15.

The laser beam transmitted through the polarization beam splitter 15 isreflected by the mirror 16 and formed in the parallel light by thecollimator lens 17. Then, the laser beam is reflected by the mirror 18,and the laser beam is further reflected toward the HD objective lens 21by the upwardly reflecting mirror 19. Then, the laser beam is convertedinto the circularly-polarized light by the quarter-wave plate 20, andthe laser beam is caused to converge onto HD by the objective lens 21.

The laser beam reflected from HD is transmitted through the quarter-waveplate 20 again, thereby converting the laser beam into thelinearly-polarized light orthogonal to the polarization direction inwhich the laser beam is incident to the optical disk. Then, the laserbeam reversely travels the optical path, and is incident to thepolarization beam splitter 15. At this point, the laser beam issubstantially totally reflected by the polarization beam splitter 15because the polarization direction of the laser beam becomes theS-polarized light with respect to the polarization beam splitter 15.Then, the anamorphic lens 27 induces the astigmatism into the laserbeam, and the laser beam converges onto the light acceptance surface(quadratic sensor) of the photodetector 28.

In performing the reproduction operation to HD, the aberration servosignal is supplied to the motor 45, the collimator lens 17 is finelymoved in the optical axis direction in the aberration correction strokerange (stroke Sc of FIG. 2B), which suppresses the aberration generatedin the laser beam on HD.

A reproduction operation of the optical disk apparatus will be describedwith reference to FIG. 6.

When the reproduction operation is started, the semiconductor laser 11is turned on (S101), and the lens holder 41 is moved to the firstposition (S102). Therefore, the optical disk to be reproduced isirradiated with the laser beam through the BD objective lens 26. At thispoint, the collimator lens 22 is located at the initial position in thestroke Sa of FIG. 2A.

Then, the objective lens holder 31 is moved in the focus direction totry the focus pull-in of the laser beam to the optical disk to bereproduced (S103). In the case where BD is the optical disk to bereproduced, an S-shape curve having sufficient waveform amplitudeappears on the focus error signal to enables the focus pull-in (YES inS104). In this case, the microcomputer 55 determines that BD is theoptical disk to be reproduced, and the microcomputer 55 causes the servocircuit 53 to perform a BD servo process (S105). Therefore, the servo(focus servo and tracking servo) is applied to the BD objective lens 26,and the aberration servo is applied to the collimator lens 22. Then, thereproduction process is performed to the optical disk (S106).

On the other hand, when BD is not the optical disk to be reproduced, theS-shape curve having the sufficient waveform amplitude does not appearon the focus error signal due to the difference in cover layer, and thefocus pull-in is not enabled (NO in S104). In this case, themicrocomputer 55 determines that BD is not the optical disk to bereproduced, and the microcomputer 55 moves the lens holder 41 to thesecond position (S107). Therefore, the lens holder 46 is displacedagainst the biasing force of the spring 47, and the collimator lens 22is located at the initial position of the stroke Sc of FIG. 2B, wherebythe optical disk to be reproduced is irradiated with the laser beamthrough the HD objective lens 21.

Then, the microcomputer 55 re-tries the focus pull-in of the laser beamto the optical disk to be reproduced (S108). When HD is the optical diskto be reproduced, the S-shape curve having the sufficient waveformamplitude appears on the focus error signal to enables the focus pull-in(YES in S109). In this case, the microcomputer 55 determines that HD isthe optical disk to be reproduced, and the microcomputer 55 causes theservo circuit 53 to perform a HD servo process (S110). Therefore, theservo (focus servo and tracking servo) is applied to the HD objectivelens 21, and the aberration servo is applied to the collimator lens 17.Then, the reproduction process is performed to the optical disk (S111).

When the S-shape curve having the sufficient waveform amplitude does notappear on the focus error signal in the focus pull-in in Step S108, themicrocomputer 55 determines that neither BD nor HD is the optical diskto be reproduced, and the microcomputer 55 stops the reproductionoperation to the optical disk (S112). In this case, a user is informedof a disk error by ejecting the optical disk or by displaying errordisplay on a monitor.

Thus, according to the embodiment, the half-wave plates 13 and 14 areinserted in and retracted from the optical path using the actuatordriving the collimator lens 22, and the target to which the laser beamis incident is switched between the BD objective lens 26 and the HDobjective lens 21. Therefore, the need for the additional configurationfor driving the half-wave plate is eliminated to achieve the simpleconfiguration of the optical pickup device. Because the inexpensivehalf-wave plates 13 and 14 are used as the optical path switchingfunction, the cost increase can be suppressed in the optical pickupdevice. Because the optical paths are switched only by controlling thedrive of the motor 45, the circuit configuration and the control processbecome simplified on the optical disk apparatus side.

Additionally, according to the embodiment, the gaps are provided betweenthe supported portion 41 c and the supported portions 46 a and 46 bshown in FIGS. 2A and 2B, which allows the drive stroke of the lensholder 46 to be suppressed and to shorten the optical path between themirrors 16 and 18. Therefore, even if the large optical path is notensured between the mirrors 16 and 18 due to the layout of the opticalcomponents, according to the embodiment, the collimator lens 17 cansmoothly be driven by the common motor 45.

Accordingly, the embodiment provides the optical pickup device which cansmoothly sort the laser beam into the two objective lenses 21 and 26with the simple configuration and the optical disk apparatus into whichthe optical pickup device is incorporated.

The present invention is not limited to the embodiment, but variousmodifications can be made.

In the embodiment, the polarization direction of the laser beam isswitched between the P-polarized light and the S-polarized light withrespect to the polarization beam splitter 15 using the two half-waveplates 13 and 14. Alternatively, as shown in FIGS. 7A and 7B, thepolarization direction of the laser beam may be switched between theP-polarized light and the S-polarized light with respect to thepolarization beam splitter 15 using one half-wave plate 60. In thiscase, the polarization direction of the laser beam transmitted throughthe half-wave plate 12 is adjusted so as to become the P-polarized lightwith respect to the polarization beam splitter 15. The half-wave plate60 is adjusted such that the polarization direction of the laser beamtransmitted through the half-wave plate 60 becomes the S-polarizedlight.

In the configuration shown in FIGS. 7A and 7B, the transparent plate 61is inserted in the optical path when the lens holder 41 is moved to thesecond position. Alternatively, even if the laser beam passes throughthe simple space without particularly providing the transparent plate61, the polarization direction of the laser beam may be switched betweenthe P-polarized light and the S-polarized light only by inserting andretracting the half-wave plate 60 in and from the optical path. However,in the case of the simple space, a difference in optical path length isgenerated between the laser beam passing through the half-wave plate 60and the laser beam passing through the space, and the resultantconvergent positions of both the laser beams are shifted backward andforward on the light acceptance surface of the photodetector 28.Therefore, both the laser beams are hardly accepted by the one lightacceptance surface.

In the configuration shown in FIGS. 7A and 7B, a transparent plate 61 isprovided to solve such disadvantages. The transparent plate 61 has athickness such that the laser beam becomes the same optical path lengthas the case in which the laser beam passes through the half-wave plate60. The provision of the transparent plate 61 eliminates the differencein optical path length between the case in which the laser beam istransmitted through the half-wave plate 60 and the case in which thelaser beam passes through the transparent plate 61, so that theconvergent position of both the laser beams can be matched with eachother on the light acceptance surface of the photodetector 28.Therefore, both the laser beams can smoothly be accepted on the commonlight acceptance surface.

Additionally, the HD objective lens 21 and the BD objective lens 26 maybe disposed as shown in FIGS. 8A and 8B. In this case, the mirrors 18and 23 of FIGS. 1A and 1B can be omitted to achieve the simpleconfiguration and the reduced number of components.

In the embodiment, the tracking error signal (TE) is generated by theone-beam push pull. In the case where the optical disk apparatus canrecord the data in the optical disk, the tracking error signal can alsobe generated by a DPP (Deferential Push Pull) method in which the threebeams are used. In this case, as shown in FIG. 9, the half-wave plate 12of FIGS. 1A and 1B is replaced by a half-wave plate 62 in which athree-beam diffraction grating in the surface thereof. The half-waveplate 62 has both a function of adjusting the polarization direction ofthe laser beam in the direction shown in FIG. 1C and a function ofdividing the laser beam from the semiconductor laser 11 into three beamsby diffraction.

Because BD differs from HD in a track pitch, an in-line pattern isapplied to a pattern of the three-beam diffraction grating. Therefore,the light reflected from the optical disk can be accepted by the commonlight acceptance surface regardless of whether the optical disk to bereproduced is BD or HD. Because the in-line DPP method is well-knowntechnique the description is omitted.

FIG. 10 shows a configuration of the signal amplifying circuit 51 inwhich the DPP method is adopted. Adding circuits 111 to 116, subtractingcircuits 117 and 119, and a multiplication circuit 118 are addedcompared with the case of FIG. 4. Quadratic sensors E to G and I to Lare added to the photodetector 28 to accept sub-beams.

Assuming that A to L are signals outputted from the quadratic sensors Ato L, the tracking error signal (TE) is generated by the computation ofTE=(A+B)−(C+D)− α{(E+I+F+J)−(G+K+H+L)}. The focus error signal (FE) andthe reproduction signal (RF) are generated in the same way as theembodiment.

In the embodiment, the half-wave plates 13 and 14 are moved in the samedirection as the optical axis of the laser beam reflected by thepolarization beam splitter 15. Alternatively, as shown in FIG. 11, thehalf-wave plates 13 and 14 may be moved in the same direction as theoptical axis of the laser beam transmitted through the polarization beamsplitter 15. In this case, the collimator lenses 17 and 22 are displacedin the X-axis direction to suppress the aberration generated in thelaser beam. An opening 41 d is formed in the tongue piece 41 a of thelens holder 41 so as not to obstruct the laser beam traveling from thepolarization beam splitter 15 to the anamorphic lens 27. As shown inFIG. 11, the arrangement of the semiconductor laser 11 and the half-waveplate 12 is changed, and a mirror 63 is added to guide the laser beamtransmitted through the half-wave plate 13 or 14 to the polarizationbeam splitter 15.

In the embodiment, the present invention is applied to the opticalpickup device compatible with BD and HD and the optical disk apparatusinto which the optical pickup device is incorporated. The presentinvention can also be applied to other compatible optical pickup devicesas appropriate. In the above description, the optical path switchingwave plate is provided in the actuator displacing the collimator lens.Alternatively, the optical path switching wave plate may be provided inthe actuator displacing other optical elements such as an expander lens.In the embodiment, the polarization direction of the laser beam isadjusted using the half-wave plate 12. Alternatively, the polarizationdirection of the laser beam may be adjusted by rotating thesemiconductor laser 11 about the optical axis.

Various changes and modifications can be made without departing from thescope of the present invention.

1. An optical pickup device comprising: a laser source which emits alaser beam having a predetermined wavelength; first and second objectivelenses which cause the laser beam to converge onto a recording medium; apolarization beam splitter which is disposed between the laser sourceand the first and second objective lenses; first and second opticalsystems which guide the two laser beams split by the polarization beamsplitter to the first and second objective lenses respectively; firstand second optical elements which are disposed in the first and secondoptical systems respectively, the first and second optical elementsbeing moved in optical axis directions of the laser beams to adjustoptical characteristics of the laser beams respectively; a firstactuator which supports a first holder holding the first optical elementwhile the first holder can be displaced in the optical axis direction ofthe laser beam; a second actuator which supports a second holder holdingthe second optical element while the second holder can be displaced inthe optical axis direction of the laser beam; a driving portion whichimparts a driving force to the first actuator; a transfer mechanismwhich transfers the driving force to the second actuator such that adrive stroke is smaller than that of the first actuator; and a waveplate which is inserted in and retracted from an optical path betweenthe laser source and the polarization beam splitter to change thepolarization direction of the laser beam incident to the polarizationbeam splitter, wherein the first and second optical elements are movedin a direction in which the wave plate is inserted and retracted, thewave plate is disposed in a support portion integral with the firstholder, the first actuator moves the first holder in both a first strokefor optical characteristic adjustment with the first optical element anda second stroke exceeding the first stroke, the first holder is movedbetween the first stroke and the second stroke to insert and retract thewave plate in and from the optical path, the polarization direction ofthe laser beam incident to the polarization beam splitter is adjustedsuch that the laser beam is guided to the first optical system, when thefirst holder is located in the first stroke, and the second holder islocated in the stroke for optical characteristic adjustment with thesecond optical element while the polarization direction of the laserbeam incident to the polarization beam splitter is adjusted such thatthe laser beam is guided to the second optical system, when the firstholder is located in the second stroke.
 2. The optical pickup deviceaccording to claim 1, wherein the first and second optical elements arelenses for correcting aberration generated in the laser beam.
 3. Theoptical pickup device according to claim 1, wherein the wave plateincludes first and second wave plate regions where the laser beam isformed in P-polarized light and S-polarized light with respect to thepolarization beam splitter, and a target inserted in the optical path isswitched between the first and second wave plate regions based onwhether the first holder is located in the first stroke or the secondstroke.
 4. The optical pickup device according to claim 1, wherein thepolarization direction of the laser beam becomes P-polarized light orS-polarized light with respect to the polarization beam splitter beforebeing incident to the wave plate, the wave plate includes a wave plateregion where the polarization direction of the laser beam is rotated byabout 90° and a transparent plate region having a thickness of anoptical path length identical to that of the wave plate region, and atarget inserted in the optical path is switched between the wave plateregion and the transparent plate region based on whether the firstholder is located in the first stroke or the second stroke.
 5. Anoptical disk apparatus comprising: an optical pickup device; and a servocircuit which controls the optical pickup device, wherein the opticalpickup device including: a laser source which emits a laser beam havinga predetermined wavelength; first and second objective lenses whichcause the laser beam to converge onto a recording medium; a polarizationbeam splitter which is disposed between the laser source and the firstand second objective lenses, first and second optical systems whichguide the two laser beams split by the polarization beam splitter to thefirst and second objective lenses respectively; first and second opticalelements which are disposed in the first and second optical systemsrespectively, the first and second optical elements being moved inoptical axis directions of the laser beams to adjust opticalcharacteristics of the laser beams respectively; a first actuator whichsupports a first holder holding the first optical element while thefirst holder can be displaced in the optical axis direction of the laserbeam; a second actuator which supports a second holder holding thesecond optical element while the second holder can be displaced in theoptical axis direction of the laser beam; a driving portion whichimparts a driving force to the first actuator; a transfer mechanismwhich transfers the driving force to the second actuator such that adrive stroke is smaller than that of the first actuator; and a waveplate which is inserted in and retracted from an optical path betweenthe laser source and the polarization beam splitter to change thepolarization direction of the laser beam incident to the polarizationbeam splitter, wherein the first and second optical elements are movedin a direction in which the wave plate is inserted and retracted, thewave plate is disposed in a support portion integral with the firstholder, the first actuator moves the first holder in both a first strokefor optical characteristic adjustment with the first optical element anda second stroke exceeding the first stroke, the first holder is movedbetween the first stroke and the second stroke to insert and retract thewave plate in and from the optical path, the polarization direction ofthe laser beam incident to the polarization beam splitter is adjustedsuch that the laser beam is guided to the first optical system, when thefirst holder is located in the first stroke, and the second holder islocated in the stroke for optical characteristic adjustment with thesecond optical element while the polarization direction of the laserbeam incident to the polarization beam splitter is adjusted such thatthe laser beam is guided to the second optical system, when the firstholder is located in the second stroke, and wherein the servo circuitcontrols the driving portion to adjust the optical characteristics ofthe laser beams incident to the first and second objective lenses, andthe servo circuit controls whether the laser beam is guided to the firstor second optical system.
 6. The optical disk apparatus according toclaim 5, wherein the first and second optical elements are lenses forcorrecting aberration generated in the laser beam.
 7. The optical diskapparatus according to claim 5, wherein the wave plate includes firstand second wave plate regions where the laser beam is formed inP-polarized light and S-polarized light with respect to the polarizationbeam splitter, and a target inserted in the optical path is switchedbetween the first and second wave plate regions based on whether thefirst holder is located in the first stroke or the second stroke.
 8. Theoptical disk apparatus according to claim 5, wherein the polarizationdirection of the laser beam becomes P-polarized light or S-polarizedlight with respect to the polarization beam splitter before beingincident to the wave plate, the wave plate includes a wave plate regionwhere the polarization direction of the laser beam is rotated by about90° and a transparent plate region having a thickness of an optical pathlength identical to that of the wave plate region, and a target insertedin the optical path is switched between the wave plate region and thetransparent plate region based on whether the first holder is located inthe first stroke or the second stroke.